In thrust type 35 mm film manufacturers' cassettes, such as those manufactured by Eastman Kodak Co. and Fuji Film Photo Ltd., a leading portion of a film strip is thrust from the confines of a loaded film cassette onto a take-up spool rather than having to manually extract the protruding leading portion, as is common to other conventional non-thrusting film cassettes. This is particularly advantageous in that a protruding portion of the film is not required and that a user does not have to take the time to manually extend the leading portion of the film for cinching to a take-up spool prior to image capture.
Another advantage realized using thrust type film cassettes is that a partially exposed film can be rewound into the cassette, and be extracted from the confines of the camera. The cassette can then be reloaded into a camera having a control system and associated logic for allowing the film strip to be thrust from the cassette and properly advanced to the next exposable frame prior to image capture. The features of rewinding a partially exposed film back into the cassette and for subsequent exposure of the previously unexposed film is referred to as mid-roll interrupt (MRI).
In commonly assigned U.S. patent application 4,994,828, an apparatus is described for preventing a film cartridge having previously exposed film from being reloaded into a film loading chamber of a camera. A blocking member having an engageable end is spring biased into the loading chamber and cooperates with the film status indicator of a film cartridge to prevent the cartridge from being loaded in the film chamber if the cartridge contains exposed film. When the film cartridge, however, contains unexposed, or in the case of cameras having MRI logic, partially exposed film, the blocking member is pivoted out of the chamber and the cartridge can be loaded.
In commonly assigned and concurrently filed U.S. application Ser. Nos. and 08/385,291 and 08/386,792, a sensing member cooperates with the above described blocking member to prevent the double exposure of film contained in an unblocked film cassette and loaded in the film loading chamber. The sensing member senses the presence of a film cassette in the chamber and trips a resettable switch, which allows the unexposed film in the cassette to be loaded for exposure. The reloading of film is prevented, however, until the switch is reset and subsequently reopened. Though an efficient means for preventing double exposure is described by these references, particularly for thrusting type cartridges, there is no feedback provided to the user other than disablement of the camera, leading to possible confusion and dissatisfaction.
There is a need for the user to understand the state of a camera, such as whether a cassette or cartridge and/or the film contained therein have been loaded, without recourse to opening the film loading chamber door, or first removing the film cartridge from the camera.